1. Field of the Invention
This invention relates to the field of flame retardants for polymers and to polymers rendered flame resistant therewith.
2. Description of the Prior Art
The increased use of polymeric materials, particularly in the building industry, has resulted in greatly increased interest in the fire retardancy of these materials. However, at the present time most commercially available plastics do not possess satisfactory fire retardancy and this inadequacy represents one of the major obstacles to the use of these materials.
Presently, the most widely used fire retardant chemicals are antimony trioxide and organohalogen compounds, the best known being chlorendic anhydride (1,4,5,6,7,7-hexachlorobicyclo[2.2.1]-hept-5-ene-2,3-dicarboxylic anhydrid e); tetrabromo- or tetrachlorophthalic acid; 1,4'-isopropylidenebis (2,6-dichlorophenol) [tetrachlorobisphenol A] or the corresponding bromine-containing compound; chloran, i.e., 2,3-dicarboxyl-5,8-endomethylene-5,6,7,8,9,9-hexachloro-1,2,3,4,4a,5,8,8a- octahydronaphthalene anhydride; chlorinated paraffins; and dechlorane (dihexachlorocyclopentadiene).
The foregoing halogen compounds have only limited utility in polymer compositions due to a number of disadvantages. For example, when such halogen compounds are incorporated into a polymer, various physical properties of the polymer are modified, e.g., change in melt viscosity which requires higher processing temperatures, decrease in light stability, decrease in thermal stability, increase in density, adverse effects on heat distortion point, etc.
Some of these disadvantages have been overcome by the use of halogen-containing polymers as the flame retardant additive. Typical of such polymers are 2-chlorobutadiene, polyvinylchloride, chlorinated polyethylene and chlorosulfonated polyethylene. There are also, however, serious disadvantages associated with the use of such polymers. Among these are: (1) large amounts of halogen-containing polymers are required in order to obtain satisfactory fire retardancy due to the relatively low halogen content thereof; (2) the halogen-containing polymers have low thermal stabilities; and (3) the blending of the halogen-containing polymer with the polymer to be rendered flame retardant usually requires expensive processing techniques.
In addition, it is known from U.S. Pat. No. 3,678,116 that 1,2,3,4,9,9-hexachloro-1,4-dihydro-1,4-methanonaphthalene-5,8-diol (I) is useful as a flame retardant for polymer systems such as polyesters.